[Source] Fine Silver bezel cups

Does anyone know why ready-made bezel cups for silver jewelry are
only available in sterling silver, when ready-made bezel wire is
always made of fine silver? Or perhaps I just don’t know of a source
for fine silver ready-made bezel cups. Do any of you know of such a
source?

Also, is anyone aware of a source for stamped (not cast) ready-made
square bezel cups?

Thanks,
Linda